Parallel bit interleaver

ABSTRACT

A bit interleaving method involves applying a bit permutation process to a QC LDPC codeword made up of N cyclic blocks each including Q bits, and dividing the codeword, after the bit permutation process, into a plurality of constellation words each imade up of M bits, the codeword being divided into N/M sections, each constellation word being associated with one of the N/M sections, and the bit permutation process being performed such that each of the constellation words includes one bit from each of M different cyclic blocks associated with a given section.

TECHNICAL FIELD

The present disclosure relates to the field of digital communications,and more specifically to a bit interleaver for a bit-interleaved codingand modulation system with quasi-cyclic low-density parity-check codes.

BACKGROUND ART

In recent years, bit-interleaved coding and modulation (hereinafter,BICM) systems have been used in the field of digital communications(see, for example, Non-Patent Literature 1).

BICM systems generally incorporate the following three steps.

(1) Encoding data blocks into codewords using, for example, quasi-cycliclow-density parity check (hereinafter, QC LDPC) code or similar.(2) Performing bit interleaving on the bits of each codeword.(3) Dividing each bit interleaved codeword into constellation wordshaving a number of constellation bits, and mapping the constellationwords to constellations.

CITATION LIST Patent Literature

[Patent Literature 1]

ETSI EN 302 755 V1.2.1 (DVB-T2 Standards)

SUMMARY OF INVENTION Technical Problem

Typically, efficiency is desirable in interleaving applied to thecodewords of quasi-cyclic low-density parity-check codes.

The present disclosure aims to provide an interleaving method enablingefficient interleaving to be applied to the codewords of quasi-cycliclow-density parity-check codes.

Solution to Problem

In order to achieve the above-stated aim, a bit interleaving method fora communication system using quasi-cyclic low-density parity checkcodes, comprising: a reception step of receiving a codeword of thequasi-cyclic low-density parity check codes made up of N cyclic blockseach including Q bits; a bit permutation step of applying a bitpermutation process to the codeword so as to permute the bits in thecodeword; and a division step of dividing the codeword, after the bitpermutation process, into a plurality of constellation words, each ofthe constellation words being made up of M bits and indicating one of2^(M) predetermined constellation points, wherein prior to the bitpermutation process, the codeword is divided into N/M sections, each ofthe sections including M of the cyclic blocks, and each of theconstellation words being associated with one of the N/M sections, andin the bit permutation step, the bit permutation process is applied suchthat the M bits in each of the constellation words include one bit fromeach of M different cyclic blocks in a given section associated with agiven constellation word, and such that all bits of the given sectionare mapped to only Q of the constellation words associated with thegiven section.

Advantageous Effects of Invention

The bit interleaving method of the present invention enables effectiveinterleaving to be applied to the codewords of the quasi-cycliclow-density parity-check codes.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing the configuration of a transmitterthat includes a typical BICM encoder.

FIG. 2 illustrates an example of a parity-check matrix for quasi-cycliclow-density parity check codes having a coding rate of ½.

FIG. 3 illustrates an example of a parity-check matrix forrepeat-accumulate quasi-cyclic low-density parity check codes having acoding rate of ⅔.

FIG. 4 illustrates a parity-check matrix for the repeat-accumulatequasi-cyclic low-density parity check codes of FIG. 3 after a rowpermutation.

FIG. 5 illustrates a parity-check matrix for the repeat-accumulatequasi-cyclic low-density parity check codes of FIG. 3 after a rowpermutation and a parity permutation.

FIG. 6 describes different robustness levels of the bits encoded ineight PAM symbols.

FIG. 7 is a block diagram showing the configuration of a typical bitinterleaver where the cyclic factor Q is 8, the number of cyclic blocksper low-density parity check codeword Nis 12, and the number of bits perconstellation M is 4.

FIG. 8A is a block diagram showing the configuration of a DVB-T2modulator used in the DVB-T2 standard, and FIG. 8B is a block diagramshowing the configuration of a BICM encoder for the DVB-T2 modulator ofFIG. 8A.

FIG. 9A illustrates a write process for the bits of a 16K codeword(i.e., an LDPC code where the LDPC codeword length is 16200 bits) asperformed by a column-row interleaver having twelve columns, and FIG. 9Billustrates a read process for the bits of the codeword written in themanner indicated by FIG. 9A as performed by the column-row interleaver.

FIG. 10A illustrates a write process for the bits of a 16K codeword asperformed by a column-row interleaver having eight columns, and FIG. 10Billustrates a read process for the bits of the codeword written in themanner indicated by FIG. 10A as performed by the column-row interleaver.

FIG. 11 is a block diagram showing the configuration of a bit-to-celldemultiplexer used for 16K codes of 16-QAM in the DVB-T2 standard.

FIG. 12 is a block diagram showing the configuration of a bit-to-celldemultiplexer used for 16K codes of 64-QAM in the DVB-T2 standard.

FIG. 13 is a block diagram showing the configuration of a bit-to-celldemultiplexer used for 16K codes of 256-QAM in the DVB-T2 standard.

FIG. 14 illustrates a problem occurring for 16K codes with aneight-column DVB-T2 bit interleaver.

FIG. 15 illustrates a problem occurring for 16K codes with atwelve-column DVB-T2 bit interleaver.

FIG. 16 illustrates a problem occurring for 16K codes with aneight-column DVB-T2 bit interleaver when column twisting is applied.

FIG. 17 illustrates a problem occurring for 16K codes with atwelve-column DVB-T2 bit interleaver when column twisting is applied.

FIGS. 18A and 18B respectively illustrate a first and second conditiondiscovered by the inventors enabling an extremely effective interleaverto be provided.

FIG. 19 illustrates a mapping function by an interleaver pertaining toan Embodiment.

FIG. 20 is a block diagram showing the configuration of an interleaverpertaining to an Embodiment.

FIG. 21A is a block diagram showing the configuration of a sectionpermutator performing the section permutation illustrated in FIG. 20,and FIG. 21B illustrates a mapping function of the section permutatorshown in FIG. 21A.

FIG. 22A is a block diagram showing an alternate configuration of asection permutator performing the section permutation illustrated inFIG. 20, and FIG. 22B illustrates a mapping function of the sectionpermutator shown in FIG. 22A.

FIG. 23 is a block diagram showing the configuration of an interleaverpertaining to another Embodiment.

FIG. 24 is a block diagram showing the configuration of the bitinterleaver shown in FIG. 23.

FIG. 25 is a block diagram of a transmitter pertaining to a furtherEmbodiment of the present disclosure.

FIG. 26 is a block diagram showing the configuration of a BICM encoderpertaining to a further Embodiment.

FIG. 27 is a block diagram of an example receiver, including anon-iterative BICM decoder, pertaining to a further Embodiment of thedisclosure.

FIG. 28 is a block diagram showing the configuration of a receiverincluding an iterative BICM decoder, pertaining to a further Embodiment.

FIG. 29 is a block diagram showing the configuration of an iterativeBICM decoder pertaining to a further Embodiment.

DESCRIPTION OF EMBODIMENTS Background Information

FIG. 1 is a block diagram showing the configuration of a transmitter 100that includes a typical bit-interleaved coding and modulation(hereinafter, BICM) encoder. As shown, the transmitter 100 includes aninput processor 110, a BICM encoder (in turn including a low-densityparity check (hereinafter, LDPC) encoder 120, a bit interleaver 130, anda constellation mapper 140), and a modulator 150.

The input processor 110 converts an input bitstream into blocks of apredetermined length. The LDPC encoder 120 encodes the blocks intocodewords using LDPC codes, and then transmits the codewords to the bitinterleaver 130. The bit interleaver 130 applies an interleaving processto each LDPC codeword, then divides each interleaved codeword into asequence of cell words (i.e., constellation words). The constellationmapper 140 maps each cell word (i.e., constellation word) to a sequenceof constellations (e.g., using QAM). The generic modulator 150 at theoutput includes all processing blocks from the output of the BICMencoder to a radio frequency (hereinafter, RF) power amplifier.

An LDPC code is a linear error correcting code that is fully defined bya parity-check matrix (hereinafter, PCM). A PCM is a binary sparsematrix that represents the connection of codeword bits (hereinafter alsotermed variable nodes) to the parity checks (hereinafter also termedcheck nodes). The columns and the rows of the PCM respectivelycorrespond to the variable nodes and the check nodes. In the PCM, aconnection between a variable node and a check node is represented by aone-element.

Quasi-cyclic low-density parity check (hereinafter, QC LDPC) codes areone variety of LDPC codes. QC LDPC codes have a structure that isparticularly suited to hardware implementation. In fact, most standardsin use today employ QC LDPC codes. The PCM of a QC LDPC code has aspecial configuration made up of a plurality of circulant matrices. Acirculant matrix is a square matrix in which each row is a cyclic shiftof the elements in the previous row, and has one, two, or more foldeddiagonals. Each circulant matrix has a size of Q×Q. Here, Q representsthe cyclic factor of the QC LDPC. The above-described quasi-cyclicconfiguration allows Q check nodes to be processed in parallel, which isclearly beneficial for efficient hardware implementation.

FIG. 2 shows the PCM of a QC LDPC code having a cyclic factor Q ofeight, as an example. In FIG. 2, as well as in later-described FIGS. 3and 5, the smallest squares each represent one element of the PCM, wherethe black squares are one-elements and all other squares arezero-elements. The PCM shown has circulant matrices with one or twofolded diagonals apiece. This QC LDPC code encodes a block of 8×6=48bits into a codeword of 8×12=96 bits. Accordingly, the coding rate ofthe QC LDPC is 48/96=1/2. The codeword bits are divided into a pluralityof blocks of Q bits each. The Q bit blocks are hereinafter termed cyclicblocks (or cyclic groups) for this relation to the cyclic factor of Q.

A special variety of QC LDPC codes are repeat-accumulate quasi-cycliclow-density parity check (hereinafter, RA QC LDPC) codes. RA QC LDPCcodes are well known as being easy to encode, and are therefore used ina wide variety of standards (e.g., in second-generation DVB standards,including DVB-S2, DVB-T2, and DVB-C2). The right-hand side of the PCMcorresponds to the parity bits. The one-elements therein are arranged ina staircase structure. FIG. 3 shows an example of a PCM for a RA QC LDPChaving a coding rate of ⅔.

Above, and throughout, DVB-T is an abbreviation of Digital VideoBroadcasting-Terrestrial, DVB-S2 is an abbreviation of Digital VideoBroadcasting-Second Generation Satellite, DVB-T2 is an abbreviation ofDigital Video Broadcasting-Second Generation Terrestrial, and DVB-C2 isan abbreviation of Digital Video Broadcasting-Second Generation Cable.

By applying a simple row permutation to the PCM shown in FIG. 3, thequasi-cyclic structure of the RA QC LDPC codes is revealed, with theexception of the parity portion, shown in FIG. 4. The row permutation isa simple change of the graphical representation having no influence onthe code definition.

The quasi-cyclic structure of the PCM parity portion is imparted byapplying a suitable row permutation to only the parity bits of the PCMshown in FIG. 4. This technique is widely known in the field and is usedin standards such as DVB-T2, under the name of parity interleaving or ofparity permutation. FIG. 5 shows the PCM obtained as a result ofapplying such parity permutation to the PCM shown in FIG. 4.

Typically, the bits of an LDPC codeword vary in importance, and the bitsof a constellation vary in robustness level. Mapping the bits of an LDPCcodeword to a constellation directly, i.e., without interleaving, leadsto suboptimal performance. Thus, the bits of the LDPC codeword requireinterleaving prior to mapping onto constellations.

For this purpose, the bit interleaver 130 is provided between the LDPCencoder 120 and the constellation mapper 140, as shown in FIG. 1. Bycarefully designing the bit interleaver 130, the association between thebits of the LDPC codeword and the bits encoded by the constellation isimproved, leading to improved receiver performance. Performance istypically measured using the bit-error rate (hereinafter, BER) as afunction of the signal-to-noise ratio (hereinafter, SNR).

The bits of the LDPC codeword differ in importance primarily because notall bits are necessarily involved in the same number of parity checks.The more parity checks (check nodes) a given codeword bit (variablenode) is involved in, the more important the given codeword bit is in aniterative LDPC decoding process. A further reason is that the variablenodes each have different connectivity to the cycles of a Tanner graphrepresenting the LDPC codes. Therefore, the codeword bits are likely todiffer in importance despite being involved in the same number of paritychecks. These ideas are well understood in the field. As a rule, theimportance of the variable nodes increases as the number of check nodesconnected therewith increases.

In the particular case of QC LDPC codes, all bits included in a cyclicblock of Q bits have the same number of parity checks applied thereto,and have the same connectivity to the cycles of the Tanner graph. Thus,all bits have the same importance.

Similarly, the encoded bits of a constellation are widely known to havedifferent levels of robustness. For example, a quadrature amplitudemodulation (hereinafter, QAM) constellation is made up of twoindependent pulse amplitude modulation (hereinafter, PAM) symbols, onesymbol corresponding to the real part and the other symbol correspondingto the imaginary part. The two PAM symbols each encode M bits. FIG. 6shows 8-PAM symbols using Gray encoding. As shown, the bits encoded byin each PAM symbol vary in terms of level of robustness. The differencein robustness is a result of the distance between two subsets defined byeach bit (e.g., 0 or 1) being different for each of the bits. Thegreater the distance, the more robust and reliable the bit. FIG. 6indicates that bit b3 has the highest robustness level, while bit b1 hasthe lowest robustness level.

Thus, a 16-QAM constellation encodes four bits and has two robustnesslevels. Likewise, a 64-QAM constellation encodes six bits and has threerobustness levels. Also, a 256-QAM constellation encodes eight bits andhas four robustness levels

The following parameters are hereinafter used throughout the presentdescription.

Cyclic factor: Q=8

Number of cyclic blocks per LDPC codeword: N=12

Number of bits per constellation: M=4 (i.e., 16-QAM)

Given the above parameters, the number of constellations to which eachLDPC codeword is mapped is equal to Q×N/M=24. Typically, the parametersQ and N are selected such that Q×N is equal to a multiple of M for allconstellations supported by the system.

FIG. 7 is a block diagram showing the configuration of a typicalinterleaver when the above parameters are applied. In FIG. 7, the 12cyclic blocks are labeled QB1, . . . , QB 12, and the 24 constellationsare labeled C1, . . . , C24. A bit interleaver 710 interleaves the 96bits of the LDPC codeword.

A conventional bit interleaver is known from the DVB-T2 standard (seeETSI EN 302 755). The DVB-T2 standard is a television standardpresenting improvements over the DVB-T standard, and describes asecond-generation baseline transmission system for digital televisionbroadcasting. The DVB-T2 standard gives the details of a channel codingand modulation system for broadcast television services and genericdata.

FIG. 8A is a block diagram showing the structure of a modulator used inthe DVB-T2 standard (i.e., a DVB-T2 modulator). The DVB-T2 modulator 800includes an input processor 810, a BICM encoder 820, a frame builder830, and an OFDM generator 840.

The input processor 810 converts an input bitstream into blocks of apredetermined length. The BICM encoder 820 applies BICM processing tothe input. The frame builder 830 uses input from the BICM encoder 820and the like to generate a distribution frame structure in the DVB-T2format. The OFDM generator 840 performs pilot addition, fast Fouriertransform application, guard interval insertion, and the like on thedistribution frame structure, then outputs a transmission signal in theDVB-T2 format.

The BICM used in the DVB-T2 standard is described in chapter 6 of theETSI EN 302 755 standard. The aforementioned standard is incorporatedherein by reference and explained below.

FIG. 8B is a block diagram showing the structure of the BICM encoder 820in the DVB-T2 modulator 800 illustrated in FIG. 8A. FIG. 8B omits outerBCH encoding, constellation rotation, the cell interleaver, the timeinterleaver, and the like.

The BICM encoder 820 includes an LDPC encoder 821, a bit interleaver (inturn including a parity interleaver 822 and a column-row interleaver823), a bit-to-cell demultiplexer 824, and a QAM mapper 825.

The LDPC encoder 821 encodes the blocks into codewords using LDPC codes.

The bit interleaver (which includes the parity interleaver 822 and thecolumn-row interleaver 823) performs interleaving on the bits of thecodewords. The bit-to-cell demultiplexer 824 demultiplexes theinterleaved bits of the codewords into cell words (constellation words).The QAM mapper 825 maps the cell words (constellation words) to complexQAM symbols. The complex QAM symbols are also termed cells. In fact, thebit-to-cell demultiplexer 824 may also be considered a part of the bitinterleaver. In such situations, the BICM encoder conforming to theDVB-T2 standard may be considered to have the basic structure shown inFIG. 1.

The LDPC codes used in the DVB-T2 standard are RA QC LDPC codes having acyclic factor of Q=360. Two codeword lengths are defined for the DVB-T2standard, one being 16200 bits and the other being 64800 bits. In thepresent document, LDPC codes using a codeword length of 16200 bits arereferred to as 16K codes (or as 16K LDPC codes), and LDPC codes having acodeword length of 64800 bits are referred to as 64K codes (or as 64KLDPC codes). The number of cyclic blocks per codeword is 45 for the 16Kcodes and 180 for the 64K codes. The available codes corresponding toeach block length (codeword length) are given in Tables A1 through A6 ofETSI EN 302 755 for the DVB-T2 standard.

The bit interleaver is used only for constellations larger thanquadrature phase-shift keying constellations (hereinafter, QPSK), andincludes the parity interleaver 822, the column-row interleaver 823, andthe bit-to-cell demultiplexer 824. According to the DVB-T2 standard, thebit interleaver does not include the bit-to-cell demultiplexer 824.However, the present document pertains to interleaving as applied toLDPC codes prior to constellation mapping. As such, the bit-to-celldemultiplexer 824 is treated as a part of the bit interleaver.

The parity interleaver 822 performs parity permutation on the paritybits of each codeword so as to clarify the quasi-cyclic structurethereof, as described above (see FIGS. 4 and 5).

Conceptually, the column-row interleaver 823 operates by writing thebits of each LDPC codeword column-wise in an interleaver matrix, thenreading the bits row-wise. The first bit of the LDPC codeword is writtenfirst, and is read first. After writing and before reading the LDPCcodeword bits, the column-row interleaver 823 cyclically shifts thecolumns of bits by a predetermined number of positions. This is termedcolumn twisting in the DVB-T2 standard. The number of columns Nc and thenumber of rows Nr in the interleaver matrix are given in Table 1 forseveral constellation sizes, according to the two aforementioned LDPCcodeword lengths.

TABLE 1 LDPC codeword No. of length Constellation size columns: Nc No.of rows: Nr 16200 16-QAM 8 2025 64-QAM 12 1350 256-QAM  8 2025 6480016-QAM 8 8100 64-QAM 12 5400 256-QAM  16 4050

The number of columns Nc is twice the number of bits per constellation,with the exception of 16K codes with a 256-QAM constellation. Thisexception occurs because the LDPC codeword length of 16200 is not amultiple of 16, i.e., is not twice the number of bits per 256-QAMconstellation.

The codeword bit writing process and bit reading process for 16K codesperformed by the column-row interleaver 823 is illustrated in FIGS. 9Aand 9B for twelve columns, and in FIGS. 10A and 10B for eight columns.Each of the small squares corresponds to one bit of the LDPC codeword.The blackened square represents the first bit of the LDPC codeword. Thearrows indicate the order in which the bits are written to and read fromthe interleaver matrix. For example, when the interleaver matrix hastwelve columns, the codeword bits of the 16K code are written in theorder given in FIG. 9A, namely (Row 1, Column 1), (Row 2, Column 1), . .. , (Row 1350, Column 1), (Row 1, Column 2), . . . , (Row 1350, Column12), then read in the order given in FIG. 9B, namely (Row 1, Column 1),(Row 1, Column 2), . . . , (Row 1, Column 12), (Row 2, Column 1), . . ., (Row 1350, Column 12). FIGS. 9A, 9B, 10A, and 10B do not illustratethe column twisting process.

Prior to QAM mapping, the bit-to-cell demultiplexer 824 demultiplexesthe LDPC codewords to obtain a plurality of parallel bit streams. Thenumber of streams is twice the number of encoded bits M per QAMconstellation, i.e., 2×M, with the exception of 16K LDPC codes with a256-QAM constellation. For 16K LDPC codes with a 256-QAM constellation,the number of streams equal to the number of encoded bits M per QAMconstellation. The M encoded bits per constellation are referred to asone cell word (constellation word). For the 16K LDPC codes, the numberof cell words per codeword is 16200/M, as given below.

8100 cells for QPSK,

4050 cells for 16-QAM,

2700 cells for 64-QAM, and

2025 cells for 256-QAM.

According to Table 1, given above, the number of parallel streams isequal to the number of columns in the column-row interleaver forconstellations larger than QPSK. The bit-to-cell demultiplexerscorresponding to 16-QAM constellations, 64-QAM constellations, and256-QAM constellations for 16K LDPC codes are respectively shown inFIGS. 11, 12, and 13. The bit notation used is that of the DVB-T2standard.

As shown in FIG. 11 (and FIGS. 12 and 13), the bit-to-cell demultiplexer824 includes a simple demultiplexer 1110 (also 1210, 1310) and a demuxpermutator 1120 (also 1220, 1320).

In addition to having the simple demultiplexer 1110 (1210, 1310) simplydemultiplex the LDPC codewords, to which interleaving has been applied,the bit-to-cell demultiplexer 824 also has the demux permutator 1120(1220, 1320) perform a permutation on the demultiplexed parallel bitstreams.

However, when the column-row interleaver is used (i.e., for 16-QAMconstellations or larger), the permutation applied to the bit streams isidentical to a permutation applied to the columns of the column-rowinterleaver due to the number of parallel bit streams being equal to thenumber of columns. Therefore, the permutation performed by thebit-to-cell demultiplexer 824 is regarded as a part of the bitinterleaver.

The bit interleaver used in the DVB-T2 standard essentially has twoproblems.

The first problem is that parallelism is impaired when the number ofcyclic blocks in the LDPC codeword is not a multiple of the number ofcolumns in the bit interleaver matrix. Reduced parallelism leads toincreased latency. This is especially problematic when iterative BICMdecoding is used by the receiver. This situation occurs for severalcombinations of LDPC codeword length and constellation size in theDVB-T2 standard.

FIGS. 14 and 15 illustrate the aforementioned situation for 16K LDPCcode cases where the interleaver matrix has eight and twelve columns,respectively. Eight columns are used in the interleaver matrix for16-QAM constellations and 256-QAM constellations. Twelve columns areused in the interleaver matrix for 64-QAM constellations. In FIGS. 14and 15, the grid represents an LDPC codeword, the small squares eachrepresent one bit of the LDPC codeword, the rows correspond to thecyclic blocks, and the columns correspond to bits of the same bit indexwithin a cyclic block. The blackened squares represent eighth andtwelfth bits of the first row in the interleaver matrix. For ease ofcomprehension, the number of bits per cyclic block has been reduced from360 to 72. However, this does not affect the understanding.

The second problem is that, in the DVB-T2 standard, the number ofpossible bit interleaver configurations is limited by the number ofcolumns in the bit interleaver matrix.

A further problem of the DVB-T2 bit interleaver is that the regularityand parallelism of the permutation is impaired by the column twistingprocess. FIGS. 16 and 17 respectively illustrate the same situations asFIGS. 14 and 15, with the addition of the column twisting process. Whenthe interleaver matrix has eight columns for the 16K LDPC codes, thecolumn twisting values for the columns of the DVB-T2 bit interleaver are(0, 0, 0, 1, 7, 20, 20, 21). Similarly, when the interleaver matrix hastwelve columns for the 16K LDPC codes, the column twisting values forthe columns of the DVB-T2 bit interleaver are (0, 0, 0, 2, 2, 2, 3, 3,3, 6, 7, 7).

Accordingly, a bit interleaver that reduces latency while improvingparallelism is desired. These properties are particularly important initerative BICM decoding.

(Experimenter Discoveries)

The inventor has discovered, as the fruit of prolonged experimentation,that an interleaver satisfying the following two conditions is extremelyefficient.

(Condition 1)

The M bits of each constellation are each mapped to one of M differentcyclic blocks of the LDPC codeword. This is equivalent to mapping onebit from M different cyclic blocks of the LDPC codeword to aconstellation word. This is schematically illustrated in FIG. 18A.

(Condition 2)

All constellation words mapped to the M cyclic blocks are mapped only tothat particular cyclic block. This is equivalent to mapping all M×Q bitsof the M different cyclic blocks each made up of Q bits to exactly Qconstellations. This is schematically illustrated in FIG. 18B.

The above conditions imply that exactly Q constellations are mapped toeach set of M cyclic blocks.

Embodiment 1

The following describes the details of a bit interleaver (i.e., aparallel bit interleaver) that satisfies conditions 1 and 2 given above.In the following description, processing and the units performing suchprocessing are labeled with the same reference numbers whereverapplicable.

In the present document, each group of M cyclic blocks and each group ofQ constellation words is referred to as a section (or as an interleaversection).

FIGS. 19 and 20 are block diagrams respectively illustrating the mappingfunction of a bit interleaver satisfying Conditions 1 and 2 andcorresponding to the aforementioned parameters (i.e., Q=8, M=4, N=12),and a sample configuration for such a bit interleaver.

In FIGS. 19 and 20, the QC-LDPC codewords are made up of N=12 cyclicblock, each in turn made up of Q=8 bits. Each of the 24 constellationwords is made up of M=4 bits. Each constellation word indicates one of2^(M)=16 constellation points. The bit interleaver is divided into N/M=3sections. The 24 constellation words are each associated one of thethree sections.

A bit interleaver 2000 includes a bit permutator 2010, which in turnincludes N/M (=3) section permutators 2021, 2022, and 2023, eachoperating independently. However, rather than providing three sectionpermutators, a single section permutator may, for example, be providedso as to performs the three section permutation processes describedbelow, switching therebetween over time.

The section permutators (2021, 2022, and 2023) each independentlyperform a section permutation on the 32 bits making up each of 4 cyclicblocks, such that one bit from every four cyclic blocks (i.e., QB1through QB4, QB5 through QB8, and QB9 through QB12) is mapped to eachgroup of eight constellation words (i.e., C1 through C8, C9 through C16,and C17 through C24).

Conditions 1 and 2, described above, ensure that the bit interleaver isdivisible into N/M parallel sections. The section permutations appliedto the parallel sections may all apply the same permutation rules, mayeach apply different permutation rules, or may involve a subset of thesections applying identical permutation rules while other differ.

For example, the section permutators may map the Q bits of a cyclicblock (which each have the same importance in LDPC decoding) to bitshaving the same bit index (i.e., having the same robustness level) inthe Q constellation words. For each cyclic block, the Q bits may be insequential or in permutated order. The latter case is described withreference to FIGS. 21A and 21B, while the former case is described withreference to FIGS. 22A and 22B.

FIG. 21A structurally illustrates the section permutator of FIG. 20.

The section permutator 2101 includes intra-cyclic-block permutators 2111through 2114 and a column-row permutator 2131. Rather than providingfour intra-cyclic-block permutators, for example, a singleintra-cyclic-block permutator may be provided and perform the fourintra-cyclic-block permutation processes, described later, switchingtherebetween over time.

The intra-cyclic-block permutators (2111-2114) each perform anintra-cyclic-block permutation on the Q-bit (8-bit) cyclic blocks(QB1-QB4). The intra-cyclic-block permutations applied to the cyclicblocks in each section may all apply the same permutation rules, mayeach apply different permutation rules, or may involve a subset of thesections applying identical permutation rules while other differ.

The column-row permutator 2131 performs a column-row permutation on eachgroup of M×Q (=32) bits. Specifically, the column-row permutator 2131writes the M×Q bits row-wise into a M×Q (8×4) matrix, then reads the M×Qbits column-wise therefrom, thus applying the column-row permutation.The column-row permutation applied by the column-row permutator 2131resembles the permutation applied to the 12×1350 matrix shown in FIGS.9A and 9B, where Q columns and M rows are used, the writing processoccurs column-wise, and the reading process occurs row-wise.

FIG. 21B is a structural representation of the section permutator shownin FIG. 21A. In FIG. 21 B, the constellation words of M=4 bits are eachdenoted b1 through b4.

However, a variation in which the intra-cyclic-block permutation processis not part of the section permutation process is also plausible.

For example, a section permutation implemented without executing theintra-cyclic-block permutation and a structure of mapping by the sectionpermutator are shown in FIGS. 22A and 22B. The section permutator 2201includes a column-row permutator 2131 and performs a simple column-rowpermutation. In FIG. 22B, the constellation words of M=4 bits are eachdenoted b1 through b4.

The section permutation described in FIGS. 21A, 21B, 22A and 22B may beapplied to cyclic blocks QB5-QB8 and QB9-QB12.

Advantageously, an additional cyclic block permutation may be applied tothe N cyclic blocks before the bit interleaver performs the sectionpermutation. FIG. 23 is a structural diagram of the additional cyclicblock permutation applied by the bit interleaver. In this context, thecyclic block permutation plays a role similar to that of the permutationperformed by the bit-to-cell demultiplexer in the DVB-T2 standard.

The bit interleaver 2300 shown in FIG. 23 includes a cyclic blockpermutator 2310 and a bit permutator 2010 (which in turn includessection permutators 2021-2023).

The cyclic block permutator 2310 performs cyclic block permutations2311-2318 on the cyclic blocks QB1-QB12. Here, the cyclic blockpermutations 2311-2318 all follow the same permutation rules.

The cyclic block permutation performed on the N cyclic blocks isparticularly advantageous in enabling optimized mapping of the LDPCcodeword bits onto the constellation bits, resulting in optimizedperformance.

FIG. 24 is a schematic block diagram of the bit interleaver 2300 shownin FIG. 23. The bit interleaver 2400 shown in FIG. 24 includes threestages, A, B, and C.

Stage A: (inter) cyclic block permutation

Stage B: intra-cyclic-block permutation

Stage C: column-row permutation

The (inter) cyclic block permutation is applied to the N cyclic blocksmaking up the codeword, the intra-cyclic-block permutation is applied tothe Q bits of each cyclic block, and the column-row permutation isapplied to the M×Q sections.

The bit interleaver 2400 shown in FIG. 24 includes the cyclic blockpermutator 2310 and the bit permutator 2010 (which in turn includes thesection permutators 2101-2103). The section permutator 2101 (2102, 2013)includes the intra-cyclic-block permutators 2111-2114 (2115-2118,2119-2122) and the column-row permutator 2131 (2132, 2133).

In the bit interleaver 2400, the (inter) cyclic block permutation isperformed by the cyclic block permutator 2310 (stage A), theintra-cyclic-block permutation is performed by the intra-cyclic-blockpermutators 2111-2122 (stage B), and the column-row permutation isperformed by the column-row permutators 2131-2133 (stage C).

The intra-cyclic-block permutators 2111-2122 may be removed from the bitinterleaver 2400 shown in FIG. 24, such that the bit interleaver isconfigured not to perform the intra-cyclic-block permutation. Also, thebit interleaver 2400 may perform the (inter) cyclic block permutationbefore the intra-cyclic-block permutation rather than after theintra-cyclic-block permutation, or may perform the (inter) cyclic blockpermutation before and after the intra-cyclic-block permutation.

The intra-cyclic-block permutators may have similar structures. This isadvantageous in that the intra-cyclic-block permutators are thusimplementable using identical resources (e.g., hardware blocks).Alternatively, the intra-cyclic-block permutations may consist ofcyclical shifts, which allow for efficient hardware implementation usingbarrel shifters. An implementation using the barrel shifters in the LDPCdecoder is also possible.

The following describes a transmitter that includes the bit interleaverperforming a bit interleaving process that satisfies Conditions 1 and 2,with reference to FIG. 25.

FIG. 25 is a block diagram of a transmitter pertaining to a furtherEmbodiment of the present disclosure. As shown in FIG. 25, a transmitter2500 includes a BICM encoder (which in turn includes an LDPC encoder2510, a bit interleaver 2520, and a constellation mapper 2530) and amodulator 2540.

The LDPC encoder 2510 encodes input blocks into codewords using QC-LDPCcodes, and then transmits the codewords to the bit interleaver 2520.

The bit interleaver 2520 receives the codeword of QC-LDPC code from theLDPC encoder 2510. The codeword is made up of N=12 cyclic blocks, eachcyclic block including Q=8 bits. The bit interleaver 2520 performsinterleaving on the bits of the codewords so as to permute the bits ofeach of the codewords. The bit interleaver 2520 divides the interleavedcodeword into a plurality of constellation words, each made up of M=4bits and indicating one of 2^(M)=16 constellation points, then outputsthe constellation words to the constellation mapper 2530. The bitinterleaver 2520 may apply the bit interleaving process discussed withreference to FIGS. 19 through 22A and 22B, or may apply a variant bitpermutation process. Also, the bit interleaver 2520 may apply anadditional cyclic block permutation process, such as the processdiscussed with reference to FIGS. 23 and 24 or a variation thereof.

The constellation mapper 2530 receives the constellation words from thebit interleaver 2520 and performs constellation mapping on theconstellation words so received.

The modulator 2740 generates a transmission signal using orthogonalfrequency division multiplexing (hereinafter, OFDM) or similar.

The following describes a BICM encoder that includes the bit interleaverperforming a bit interleaving process that satisfies Conditions 1 and 2,with reference to FIG. 26.

FIG. 26 is a block diagram of an example BICM encoder pertaining to afurther Embodiment of the disclosure. In FIG. 26, the BICM encoder 2600corresponds to the above-given parameters (i.e., Q=8, N=12, M=4).

The BICM encoder 2600 shown in FIG. 26 includes a main memory 2601, anLDPC controller 2611, a rotator 2612, a check node processor group 2613,a de-rotator 2614, a QB counter 2631, table A 2632, interleaver B 2633,a register group 2634, interleaver C 2635, and a mapper group 2651.

In FIG. 26, given that Q=8, the main memory 2601 reads eight bits at atime, the check node processor group 2613 includes eight check nodeprocessors, and the mapper group 2651 includes eight mappers. Also,given that M=4, the register group 2634 includes four registers.

The main memory 2601 receives a sequence of bits for transmission from,for example, the (non-diagrammed) input processor, and stores thereceived bit sequence.

The LDPC controller 2611 outputs a read address to the main memory 2601.The main memory 2601 accordingly outputs the bit sequence, eight bits ata time beginning with the lead bit, to the rotator 2612. The rotator2612 is controlled by the LDPC controller 2611 to perform apredetermined number of cyclical shifts on the eight bits suppliedthereto by the main memory 2601, and then outputs the eightcyclically-shifted bits to the check node processors of the check nodeprocessor group 2613, one bit at a time, the bits and the check nodeprocessors being in one-to-one correspondence. Each check node processerof the check node processor group 2613 is controlled by the LDPCcontroller 2611 to perform check node processing on each bit inputthereto, then outputs the results to the de-rotator 2614. The de-rotator2614 is controlled by the LDPC controller 2611 to perform apredetermined number of cyclic shifts on the eight bits received fromthe check node processor group 2613 so as to cancel the cyclic shiftapplied by the rotator 2612, and then outputs the eight shifted bits tothe main memory 2601. The LDPC controller 2611 outputs a write addressto the main memory 2601. The main memory 2601 accordingly stores theeight bits supplied thereto by the de-rotator 2614. The LDPC controller2611, the rotator 2612, the check node processor group 2613, and thede-rotator 2614 make up the BICM encoder in the LDPC encoder 2510 shownin FIG. 25.

The QB counter 2631 counts from 0 to 11 and outputs the counter value totable A 2632. The count operation of the QB counter 2631 is defined inconsideration of N=12.

Table A 2632 is a simple look-up table in which the cyclic blockpermutation rules are stored. That is, table A 2632 stores N=12 piecesof cyclic block read order information (information associating adifferent cyclic block with each of the 12 counter values from the QBcounter 2631). Table A 2632 outputs a read address to the main memory2601 such that the bits of one cyclic block (i.e., Q=8 bits)corresponding to the counter value supplied by the QB counter 2631 aresupplied from the main memory 2601 to interleaver B 2633. Thus, the mainmemory 2601 outputs the bits of one cyclic block corresponding to thecounter value of the QB counter 2631 to interleaver B 2633. Theprocessing using table A 2632 is executed as the cyclic blockpermutation process (stage A).

Interleaver B 2633 performs a predetermined number of cyclical shifts onthe bits of the cyclic block supplied by the main memory 2601, andoutputs the results to a first tier register of the register group 2634.The processing by interleaver B 2633 is executed as theintra-cyclic-block permutation process (stage B). Each register in theregister group 2634 stores one cyclic block of bits with timing matchingthe reception of a control pulse, and outputs the cyclic block of bitsbefore receiving the next control pulse.

When the QB counter 2631 performs the aforementioned process for countervalues 0 through 3, the bits of four cyclic blocks (i.e., 32 bits) areinput to interleaver C 2635. At this time, interleaver C 2635interleaves the bits of the four cyclic blocks input thereto, and themappers of the mapper group 2651 output one constellation word of bits(i.e., M=4 bits). Through the interleaving process, four bits, i.e., onefrom each of the four registers in the register group 2634, are suppliedto each mapper. This processing by interleaver C 2635 is executed as thecolumn-row permutation process (stage C).

The QB counter 2631, table A 2632, interleaver B 2633, the registergroup 2634, and interleaver C 2635 make up the bit interleaver 2520 ofthe BICM encoder shown in FIG. 25.

The mappers of the mapper group 2651 each map four bits supplied theretofrom interleaver C 2635 to a constellation, then output the results. Themapper group 2651 makes up the constellation mapper 2530 of the BICMencoder shown in FIG. 25.

For each codeword, the above-described set of processes is applied threetimes, once each for counter values 0-3, 4-7, and 8-11 of the QB counter2631.

The Embodiment depicted in FIG. 26 includes Q mappers operating inparallel. However, the mappers are also realizable as a BICM encoder soas to decrease or increase the parallelism. For example, the number ofparallel interleaver sections in the bit interleaver, i.e., the quotientof N/M, obviously may be increased so as to easily enhance parallelism.Such methods enable the parallelism to be optimized by parallelizing theQ×N/M mappers. Implementing such parallelism, without drawbacks, in thebit interleaver is beneficial.

The following describes a receiver receiving signals from a transmitterthat includes the bit interleaver performing a bit interleaving processthat satisfies Conditions 1 and 2, with reference to FIG. 27.

FIG. 27 is a block diagram of an example receiver, including anon-iterative BICM decoder, pertaining to a further Embodiment of thedisclosure. The receiver performs the transmitter operations in reverse.

The receiver 2700 shown in FIG. 27 includes a demodulator 2710 and anon-iterative BICM decoder (which in turn includes a constellationdemapper 2720, a bit deinterleaver 2730, and an LDPC decoder 2740).

The demodulator 2710 performs a demodulation process through OFDM, forexample, and outputs the demodulated results.

The constellation demapper 2720 of the non-iterative BICM decodergenerates a soft bit sequence by applying a demapping process to theinput from the demodulator 2710, and outputs the soft bit sequence sogenerated to the constellation demapper 2730. The soft bits are ameasure of probability that a given bit is a zero-bit or a one-bit.Typically, the soft bits are represented as log-likelihood ratios(hereinafter, LLRs), defined as follows.

LLR(b)=ln [p(b=0)/p(b=1)]

where p(b=0) indicates the probability of the given bit b being azero-bit, and p(b=1) represents the probability of the given bit b beinga one-bit. Of course, p(b=0)+p(b=1)=1.

The bit deinterleaver 2730 performs an interleaving process (i.e., a bitde-interleaving process) on the soft bit sequence output from theconstellation demapper 2720 so as to cancel the bit interleaving processapplied to the bit sequence by the bit interleaver 2730 in thetransmitter illustrated in FIG. 25.

The LDPC decoder 2740 receives the soft bit sequence deinterleaved bythe bit deinterleaver 2730, and performs an LDPC decoding process usingthe soft bit sequence so received.

One improved technique offering significant performance gains isiterative BICM decoding. FIG. 28 illustrates an iterative BICM decoder.

FIG. 28 is a block diagram of an example receiver, including aniterative BICM decoder, pertaining to a further Embodiment of thedisclosure. The receiver performs the transmitter operations in reverse.

As shown in FIG. 28, a receiver 2800 includes the demodulator 2710 andan iterative BICM decoder (which in turn includes the constellationdemapper 2720, the bit deinterleaver 2730, the LDPC decoder 2740, asubtractor 2760, and a bit interleaver 2750).

The receiver 2800 of FIG. 28 has the constellation demapper 2720performing a constellation demapping process, the bit deinterleaver 2730performing a bit deinterleaving process, and the LDPC decoder 2740performing an LDPC decoding process.

After one or more LDPC decoding iterations, extrinsic information,obtained by the subtractor 2760 subtracting the input to the LDPCdecoder 2740 from the output of the LDPC decoder 2740, is output to thebit interleaver 2750. The bit interleaver 2750 performs an interleavingprocess on the extrinsic information using the same interleaving rulesas those applied to the bit sequence by the bit interleaver of thetransmitter depicted in FIG. 25. The bit interleaver 2750 then feedsback the interleaved extrinsic information to the constellation demapper2720. The constellation demapper 2720 uses the extrinsic information sofed back as a-priori information to compute more reliable LLR values.The bit deinterleaver 2730 then performs an interleaving process on thenewly computed LLR values (i.e., a bit de-interleaving process) so as tocancel the bit interleaving process applied to the bit sequence by thebit interleaver in the transmitter depicted in FIG. 25 and restore theoriginal order of the bit sequence. The LDPC decoder 2740 uses the LLRvalues so de-interleaved in the LDPC decoding process.

As shown in FIG. 28, an iterative decoding loop is made up of fourelements, namely the constellation demapper 2720, the bit deinterleaver2730, the LDPC decoder 2740, and the bit interleaver 2750. The bitdeinterleaver 2730 and the bit interleaver 2750 have beneficially verylow latency, ideally zero, and low complexity. This results in a moreefficient receiver implementation. The bit deinterleaver 2730 and thebit interleaver 2750 described above satisfy both of these conditions.

FIG. 29 illustrates an iterative BICM decoder realizing very efficientparallel implementation.

FIG. 29 is a block diagram of an example BICM decoder pertaining to afurther Embodiment of the disclosure. In FIG. 29, the BICM decoder 2900corresponds to the above-given parameters (i.e., Q=8, N=12, M=4).

As shown, the BICM decoder 2900 includes a main LLR memory 2901, abuffer LLR memory 2902, an LDPC controller 2911, a rotator 2912, a checknode processor group 2913, a de-rotator 2914, a QB counter 2931, table A2932, a subtractor group 2933, interleaver B 2934, register group 2935,interleaver C 2936, a demapper group 2937, deinterleaver C 2938,register group 2939, deinterleaver B 2940, and a delayer 2941.

In FIG. 29, given that Q=8, the main LLR memory 2901 and the buffer LLRmemory 2902 each read eight LLR values at a time, the check nodeprocessor group 2913 includes eight check node processors, and thedemapper group 2951 includes eight demappers. Also, given that M=4, theregister groups 2935 and 2972 each include four registers.

The demappers in the demapper group 2937 each perform a demappingprocess on the output of a demodulator (not diagrammed), then outputsthe LLR values so obtained to deinterleaver C 2938. The demapper group2937 makes up the constellation demapper 2720 of the iterative BICMdecoder shown in FIG. 28.

Deinterleaver C 2938 applies a deinterleaving process to the LLR values(i.e., a new interleaving process cancelling the interleaving processapplied by the transmitter during stage C), then outputs thedeinterleaved LLR values to the registers of the register group 2939.Each register stores one cyclic block of LLR values (i.e., eight LLRvalues). In register group 2939, the cyclic block of LLR values storedby each register is sequentially output to a later tier such that thecontent of each register is sequentially updated. Deinterleaver B 2940applies a deinterleaving process to the cyclic block of (eight) LLRvalues (i.e., a new interleaving process cancelling the interleavingprocess applied by the transmitter during stage B), then writes theresults to the main LLR memory 2901 and the buffer LLR memory 2902 inaccordance with table A 2932 (discussed later). An interleaving processcancelling the interleaving process applied by the transmitter duringstage A is achieved by this writing to the main LLR memory 2901 and thebuffer LLR memory 2902 in accordance with the content of Table A 2932.

Thus, the main LLR memory 2901 stores the post-deinterleaving LLRvalues, and is also used by the LDPC decoder (i.e., the LDPC controller2911, the rotator 2912, the check node processor group 2913, and thede-rotator 2914). The LDPC decoding process is an iterative processinvolving one or more iterations. In each LDPC decoding iteration, theLLR values in the main LLR memory 2901 are updated. In order to computethe extrinsic information needed for iterative BICM decoding, the oldLLR values are saved in the buffer LLR memory 2902.

The following describes the LDPC decoder operations.

The LDPC controller 2911 outputs the read address to the main LLR memory2901 in accordance with the parity-check matrix of the LDPC codes. Thus,the main LLR memory 2901 sequentially outputs one cyclic block of LLRvalues to the rotator 2912. The rotator 2912 is controlled by the LDPCcontroller 2911 to perform a predetermined number of cyclical shifts onthe cyclic block of LLR values supplied sequentially by the main LLRmemory 2901, then outputs the LLR values so shifted to the check nodeprocessors of the check node processor group 2913 one at a time. Thecheck node processors of the check node processor group 2913 arecontrolled by the LDPC controller 2911 to perform a check node processon the sequence of LLR values sequentially input thereto. Next, thecheck node processors of the check node processor group 2913 arecontrolled by the LDPC controller 2911 to sequentially output the LLRvalues resulting from the check node process. The de-rotator 2914 iscontrolled by the LDPC controller 2911 to performs a predeterminednumber of cyclic shifts cancelling the cyclic shift applied to thecyclic block sequentially received from the check node processor group2913 by the rotator 2912, then sequentially outputs the shifted resultsto the main LLR memory 2901. The LDPC controller 2911 outputs the writeaddress to the main LLR memory 2901 in accordance with the parity-checkmatrix of the LDPC codes. Thus, the main LLR memory 2901 stores thecyclic block of results sequentially supplied thereto by the de-rotator2914. The LDPC controller 2911 repeatedly executes the above-describedprocessing in accordance with the parity-check matrix of the LDPC codes.

After a predetermined number of LDPC iterations, a BICM iteration isperformed. The LDPC and BICM iterations are also respectively referredto as inner and outer iterations. These two types of iterative may alsooverlap in some implementations. This enables the speed of convergenceto be increased. The BICM and LDPC decoding processes are well known inthe field, and the details thereof are thus omitted.

The QB counter 2931 counts from 0 to 11 and outputs the counter value totable A 2932. The count operation of the QB counter 2931 is defined inconsideration of N=12.

Table A 2932 is a simple look-up table in which the cyclic blockpermutation rules are stored. That is, table A 2932 stores N=12 piecesof cyclic block read (and write) order information (i.e., withinformation associating a different cyclic block with each of the 12counter values from the QB counter 2631). Table A 2932 outputs the readaddress to the main LLR memory 2901 and to the buffer LLR memory 2902such that one cyclic block of LLR values corresponding to the countervalue supplied by the QB counter 2931 are supplied to the subtractorgroup 2933 by the main LLR memory 2901 and to the buffer LLR memory2902. Thus, the main LLR memory 2901 and the buffer LLR memory 2902 eachoutput a cyclic block of LLR values corresponding to the counter valueof the QB counter 2931 to the subtractor 2933. The delayer 2941 makes adelay adjustment such that the position of the LLR value read from themain LLR memory 2901 and the buffer LLR memory 2902 match the writeposition of the same LLR values to the main LLR memory 2901 and thebuffer LLR memory 2902. The processing using table A 2932 is executed asthe cyclic block permutation process (stage A).

The subtractor 2933 in the subtractor group subtracts the output of thebuffer LLR memory 2902 from the output of the main LLR memory 2901, thenoutputs the extrinsic information for one cyclic block thus obtained(i.e., eight pieces of extrinsic information) to interleaver B 2934.

Interleaver B 2634 performs a predetermined number of cyclical shifts onthe pieces of extrinsic information for one of the cyclic blockssupplied by the subtractor 2933, and outputs the results to a first tierregister of the register group 2935. The processing performed byinterleaver B 2934 corresponds to the intra-cyclic-block permutation(stage B). Each register in the register group 2935 stores eight bitswith timing matching the reception of a control pulse, and outputs theeight bits before receiving the next control pulse.

When the QB counter 2631 performs the aforementioned process for countervalues 0 through 3, the extrinsic information for four cyclic blocks(i.e., 32 pieces of extrinsic information) are input to interleaver C2936. At this time, interleaver C 2936 performs an interleaving processon the extrinsic information input thereto for four cyclic blocks, thenoutputs one constellation word of extrinsic information (i.e., M=4pieces of extrinsic information) to each demapper of the demapper group2937. Through the interleaving process, the four pieces of extrinsicinformation are supplied to the demappers of the demapper group 2951from the four registers in register group 2935, one at a time. Thisprocessing by interleaver C 2936 is executed as the column-rowpermutation process (stage C).

The QB counter 2931, table A 2932, interleaver B 2934, the registergroup 2935, and interleaver C 2936 make up the bit interleaver 2750 ofthe BICM decoder shown in FIG. 28.

The demappers of the demapper group 2937 uses the four pieces ofextrinsic information supplied by interleaver C 2936 as a-prioriinformation to perform a demapping process, then output the resultingLLR values to deinterleaver C 2938.

Deinterleaver C 2938 applies a deinterleaving process to the LLR values(i.e., a new interleaving process cancelling the interleaving processapplied by the transmitter during stage C), then outputs thedeinterleaved LLR values to the registers of the register group 2939.Each register stores one cyclic block of LLR values (i.e., eight LLRvalues). In register group 2939, the cyclic block of LLR values storedby each register is sequentially output to a later tier such that thecontent of each register is sequentially updated. Deinterleaver B 2940applies a deinterleaving process to the cyclic block of (eight) LLRvalues (i.e., a new interleaving process cancelling the interleavingprocess applied by the transmitter during stage B), then writes theresults to the main LLR memory 2901 and the buffer LLR memory 2902. Themain LLR memory 2901 and the buffer LLR memory 2902 receive the writeaddress from table A 2932 via the delayer 2941, then store one cyclicblock of LLR values (i.e., eight LLR values) received from thedeinterleaver 2940 in accordance with the received write address. Aninterleaving process cancelling the interleaving process applied by thetransmitter during stage A (i.e., a deinterleaving process) is achievedby this writing in accordance with the content of table A 2932.

For each codeword, the above-described set of processes is applied threetimes, once each for counter values 0-3, 4-7, and 8-11 of the QB counter2931.

The QB counter 2931, table A 2932, deinterleaver B 26938, the registergroup 2939, and interleaver C 2940 make up the bit interleaver 2730 ofthe BICM decoder shown in FIG. 28.

Interleaver B 2934 and deinterleaver B 2940 are reconfigurable. Thisrequires a certain hardware cost, but this cost is minimized byattentive design. Interleaver C 2936 and deinterleaver 2938 implementthe column-row permutation. This permutation is uniform for apredetermined constellation size. Thus, the cost of implementation isreduced.

The Embodiment depicted in FIG. 29 includes Q demappers operating inparallel. However, the demappers are also realizable as an iterativeBICM decoder by decreasing or increasing the parallelism. For example,the number of parallel interleaver sections in the bit interleaver,i.e., the quotient of N/M, obviously may be increased so as to easilyenhance parallelism. Such methods enable the parallelism to be optimizedby parallelizing the Q×N/M demappers. The above-described bitinterleaver has the merit of being implementable with such parallelismwithout trouble.

(Supplement 1)

The present disclosure is not limited to the Embodiments describedabove. Provided that the aims of the invention and accompanying aims areachieved, other variations are also possible, such as the following.

(1) Embodiment 1 is described above using the parameters N=12, Q=8, andM=4. However, no limitation to the parameters N, M, and Q is intended.Here, N may be any multiple of M. When N is two or more times M, theprocessing by the bit interleaver is divisible into a plurality ofsections.(2) In the above-described Embodiments, the constellations are describedas 16-QAM (i.e., M=4). However, the constellations may be specified byother modulation methods such as QPSK and QAM, such as the circularconstellations employed in the DVB-S2 standard, higher-dimensionalconstellations, and so on.(3) The methods and devices discussed in the above Embodiments may beimplemented as software or as hardware. No particular limitation isintended in this regard. Specifically, the above-described Embodimentsmay be implemented as a computer-readable medium having embodied thereoncomputer-executable instructions that are adapted for allowing acomputer, a microprocessor, a microcontroller, and the like to executethe above-described methods. Also, the above-described Embodiments maybe implemented as an Application-Specific Integrated Circuit (ASIC) oras an Field Programmable Gate Array (FPGA).

(Supplement 2)

The bit interleaving method, bit interleaver, bit deinterleaving method,bit deinterleaver, and decoder of the present disclosure, and theeffects thereof, are described below.

In a first aspect of a bit interleaving method, a bit interleavingmethod for a communication system using quasi-cyclic low-density paritycheck codes comprises: a reception step of receiving a codeword of thequasi-cyclic low-density parity check codes made up of N cyclic blockseach including Q bits; a bit permutation step of applying a bitpermutation process to the codeword so as to permute the bits in thecodeword; and a division step of dividing the codeword, after the bitpermutation process, into a plurality of constellation words, each ofthe constellation words being made up of M bits and indicating one of2^(M) predetermined constellation points, wherein prior to the bitpermutation process, the codeword is divided into N/M sections, each ofthe sections including M of the cyclic blocks, and each of theconstellation words being associated with one of the N/M sections, andin the bit permutation step, the bit permutation process is applied suchthat the M bits in each of the constellation words include one bit fromeach of M different cyclic blocks in a given section associated with agiven constellation word, and such that all bits of the given sectionare mapped to only Q of the constellation words associated with thegiven section.

In another aspect, a first bit interleaver for a communication systemusing quasi-cyclic low-density parity check codes comprises: a bitpermutation unit receiving a codeword of the quasi-cyclic low-densityparity check codes made up of N cyclic blocks each including Q bits,applying a bit permutation process to the codeword so as to permute thebits in the codeword, and dividing the codeword, for output after thebit permutation process, into a plurality of constellation words, eachof the constellation words being made up of M bits and indicating one of2^(M) predetermined constellation points, wherein prior to the bitpermutation process, the codeword is divided into N/M sections, each ofthe sections including M of the cyclic blocks, and each of theconstellation words being associated with one of the N/M sections, andthe bit permutation unit applies the bit permutation process such thatthe M bits in each of the constellation words include one bit from eachof M different cyclic blocks in a given section associated with a givenconstellation word, and such that all bits of the given section aremapped to only Q of the constellation words associated with the givensection.

Accordingly, a bit interleaving process having high parallelism isrealizable.

In a second aspect of the bit interleaving method, the bit permutationstep includes a section permutation step of applying a sectionpermutation process independently to each of the N/M sections so as topermute the bits in each of the sections.

Also, in a second aspect of a bit interleaver, the bit permutation unitincludes a section permutation unit applying a section permutationprocess independently to each of the NIM sections so as to permute thebits in each of the sections.

Accordingly, a plurality of folding section permutation processes areexecutable in parallel.

In a third aspect of the bit interleaving method, in the sectionpermutation step, the section permutation process is applied such thatthe Q bits in the given cyclic block are each mapped to a bit of anidentical bit index in the Q constellation words associated with thegiven section that corresponds to the given cyclic block.

Also, in a third aspect of a bit interleaver, the section permutationunit applies the section permutation process such that the Q bits in thegiven cyclic block are each mapped to a bit of an identical bit index inthe Q constellation words associated with the given section thatcorresponds to the given cyclic block.

Accordingly, bits of the codeword having the same importance are mappedto bits of the constellation word having the same robustness level,allowing a matching of importance and robustness level. For example, thebit of the codeword having the highest importance may be mapped to a bitof the constellation word having the highest robustness level. In such acase, high reliability is achieved at reception time for the bit of thecodeword having the highest importance, resulting in greater receptioncapability.

In a fourth aspect of the bit interleaving method, the sectionpermutation step includes a column-row permutation step of applying acolumn-row permutation process to the M×Q bits in each of the sections,so as to permute the bits in each of the sections.

In a fifth aspect of the bit interleaving method, the sectionpermutation step includes, for each of the N/M sections: anintra-cyclic-block permutation step of applying an intra-cyclic-blockpermutation process independently to each of the cyclic blocks so as topermute the bits in each of the cyclic blocks, and a column-rowpermutation step of applying a column-row permutation process to the M×Qbits in each of the sections, so as to permute the M×Q bits after thecyclic block permutation process.

In a sixth aspect of the bit interleaving method, the column-rowpermutation process is equivalent to writing the M×Q bits row-wise intoa matrix having Q columns and M rows, then reading the M×Q bitscolumn-wise.

Also, in a fourth aspect of a bit interleaver, the section permutationunit includes a column-row permutation unit applying a column-rowpermutation process to the M×Q bits in each of the sections, so as topermute the bits in each of the sections.

Also, in a fifth aspect of a bit interleaver, the section permutationunit applies, to each of the N/M sections: an intra-cyclic-blockpermutation process, applied independently to each of the cyclic blocksso as to permute the bits in each of the cyclic blocks, and a column-rowpermutation process, applied to the M×Q bits in each of the sections soas to permute the M×Q bits after the cyclic block permutation process.

Accordingly, a column-row permutation is used in the section permutationprocess, thus enabling the realization of an extremely efficient sectionpermutation process.

In a seventh aspect of the bit interleaving method, the bit interleavingmethod of the first aspect further comprises a cyclic block permutationstep of applying a cyclic block permutation process to the cyclic blocksin the codeword so as to permute the cyclic blocks within the codeword.

Also, in a sixth aspect of a bit interleaver, the bit interleaver of thefirst aspect further comprises a cyclic block permutation unit applyinga cyclic block permutation process to the cyclic blocks in the codewordso as to permute the cyclic blocks within the codeword.

Accordingly, the bits in the codeword are optimally mapped to the bitsin the constellation word, thus enabling overall BICM optimization.

In a further aspect, a bit deinterleaving method for deinterleaving abit stream in a communication system using quasi-cyclic low-densityparity check codes comprises: a reception step of receiving a bitsequence made up of N×Q bits; and a reverse bit permutation step ofapplying a reverse bit permutation process to the received bit sequenceso as to permute the bits in the bit sequence in order to restore thecodeword of the quasi-cyclic low-density parity check codes, wherein thereverse bit permutation process reverses the bit permutation process inthe bit interleaving method of the first aspect.

In an alternate aspect, a bit deinterleaver for deinterleaving a bitstream in a communication system using quasi-cyclic low-density paritycheck codes comprises: a reverse bit permutation unit receiving a bitsequence made up of N×Q bits, and applying a reverse bit permutationprocess to the received bit sequence so as to permute the bits in thebit sequence in order to restore a codeword of the quasi-cycliclow-density parity check codes, wherein the reverse bit permutationprocess reverses the bit permutation process applied by the bitinterleaver of the first aspect.

In another aspect, a decoder for a bit interleaving and demodulatingsystem using quasi-cyclic low-density parity check codes comprises aconstellation demapper generating a soft bit sequence indicating aprobability of a corresponding bit being one of a zero-bit and aone-bit; the bit deinterleaver of the alternate aspect deinterleavingthe soft bit sequence; and a low-density parity check decoder decodingthe deinterleaved soft bit sequence.

In yet another aspect, the decoder of the other aspect furthercomprises: a subtraction unit subtracting input to the low-densityparity check decoder from output of the low-density parity checkdecoder; and the bit interleaver of the first aspect, providing thedifference from the subtraction unit to the constellation demapper asfeedback.

Accordingly, a bit interleaving process having high parallelism isrealizable.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a bit interleaver in abit-interleaved coding and modulation system used for quasi-cycliclow-density parity codes, and to a bit deinterleaver corresponding tosuch a bit interleaver.

REFERENCE SIGNS LIST

-   2000, 2300, 2400 Bit interleaver-   2010 Bit permutator-   2021-2023 Section permutator-   2101, 2201 Bit permutator-   2111-2122 Intra-cyclic-block permutator-   2131-2133 Column-row permutator-   2310 Cyclic block permutator-   2500 Transmitter-   2510 LDPC encoder-   2520 Bit interleaver-   2530 Constellation mapper-   2700, 2800 Receiver-   2710 Constellation demapper-   2720 Bit deinterleaver-   2730 LDPC decoder-   2740 Subtractor-   2750 Bit interleaver

1. A transmitting method for transmitting a codeword generated based ona quasi-cyclic low-density parity check coding scheme, including arepeat-accumulate quasi-cyclic low-density parity check coding scheme,the transmitting method comprising: a cyclic block permutation step ofapplying a cyclic block permutation process to a codeword made up of Ncyclic blocks each consisting of Q bits, to reorder the cyclic blocks inaccordance with a cyclic block permutation rule defining a reordering ofthe cyclic blocks; a bit permutation step of applying a bit permutationprocess to the codeword after the cyclic block permutation process, toreorder the bits of the codeword in accordance with a bit permutationrule defining a reordering of the bits; a dividing step of dividing thecodeword after the bit permutation process into a plurality ofconstellation words, each of the constellation words being made up of Mbits, and a transmitting step of transmitting a transmitting signalgenerated from the constellation words, wherein N is a multiple of M,the bit permutation rule defines the reordering of the bits of thecodeword after the cyclic block permutation process, such that the Qbits in each of the N cyclic blocks are each allocated to a bit of anidentical bit index in Q constellation words and the Q constellationwords are each made up of one bit in each of M cyclic blocks, the Mcyclic blocks being common to the Q constellation words, and the bitindex of the bit in each of the constellation words to which the bits ineach of the cyclic blocks are allocated is determined in accordance withthe cyclic block permutation rule.
 2. A transmitter for transmitting acodeword generated based on a quasi-cyclic low-density parity checkcoding scheme, including a repeat-accumulate quasi-cyclic low-densityparity check coding scheme, the transmitter comprising: a cyclic blockpermutator that, in operation, applies a cyclic block permutationprocess to a codeword made up of N cyclic blocks each consisting of Qbits, to reorder the cyclic blocks in accordance with a cyclic blockpermutation rule defining a reordering of the cyclic blocks; a bitpermutator that, in operation, applies a bit permutation process to thecodeword after the cyclic block permutation process, to reorder the bitsof the codeword in accordance with a bit permutation rule defining areordering of the bits; a divider that, in operation, divides thecodeword after the bit permutation process into a plurality ofconstellation words, each of the constellation words being made up of Mbits, and a transmitter that, in operation, transmits a transmittingsignal generated from the constellation words, wherein N is a multipleof M, the bit permutation rule defines the reordering of the bits of thecodeword after the cyclic block permutation process, such that the Qbits in each of the N cyclic blocks are each allocated to a bit of anidentical bit index in Q constellation words and the Q constellationwords are each made up of one bit in each of M cyclic blocks, the Mcyclic blocks being common to the Q constellation words, and the bitindex of the bit in each of the constellation words to which the bits ineach of the cyclic blocks are allocated is determined in accordance withthe cyclic block permutation rule.
 3. A receiving method for receiving atransmitting signal generated by modulating N×Q/M constellation words,the constellation words being generated by applying a bit reorderingprocess to a codeword generated based on a quasi-cyclic low-densityparity check coding scheme, including a repeat-accumulate quasi-cycliclow-density parity check coding scheme, and dividing bits of thecodeword for each M bits, the codeword being made up of N cyclic blockseach including Q bits, the bit reordering process comprising: a cyclicblock permutation process of reordering the cyclic blocks of thecodeword in accordance with a cyclic block permutation rule defining areordering of the cyclic blocks; and a bit permutation process ofreordering the bits of the codeword after the cyclic block permutationprocess in accordance with a bit permutation rule defining a reorderingof the bits, wherein N is a multiple of M, the bit permutation ruledefines the reordering of the bits of the codeword after the cyclicblock permutation process, such that the Q bits in each of the N cyclicblocks are each allocated to a bit of an identical bit index in Qconstellation words and the Q constellation words are each made up ofone bit in each of M cyclic blocks, the M cyclic blocks being common tothe Q constellation words, the bit index of the bit in each of theconstellation words to which the bits in each of the cyclic blocks areallocated is determined in accordance with the cyclic block permutationrule, and the receiving method comprising a receiving step of receivinga received signal, the received signal being generated by receiving thetransmitting signal transmitted from a transmitter, a demodulating stepof generating a demodulated signal by demodulating the received signal,which has been transmitted by modulating the N×Q/M constellation words;and a decoding step of decoding the demodulated signal in accordancewith the cyclic block permutation rule and the bit permutation rule togenerate data before coding according to the quasi-cyclic low-densityparity check coding scheme.
 4. A receiver for receiving a transmittingsignal generated by modulating N×Q/M constellation words, theconstellation words being generated by applying a bit reordering processto a codeword generated based on a quasi-cyclic low-density parity checkcoding scheme, including a repeat-accumulate quasi-cyclic low-densityparity check coding scheme, and dividing bits of the codeword for each Mbits, the codeword being made up of N cyclic blocks each including Qbits, the bit reordering process comprising: a cyclic block permutationprocess of reordering the cyclic blocks of the codeword in accordancewith a cyclic block permutation rule defining a reordering of the cyclicblocks; and a bit permutation process of reordering the bits of thecodeword after the cyclic block permutation process in accordance with abit permutation rule defining a reordering of the bits, wherein N is amultiple of M, the bit permutation rule defines the reordering of thebits of the codeword after the cyclic block permutation process, suchthat the Q bits in each of the N cyclic blocks are each allocated to abit of an identical bit index in Q constellation words and the Qconstellation words are each made up of one bit in each of M cyclicblocks, the M cyclic blocks being common to the Q constellation words,the bit index of the bit in each of the constellation words to which thebits in each of the cyclic blocks are allocated is determined inaccordance with the cyclic block permutation rule, and the signalprocessor comprising a receiver that, in operation, receives a receivedsignal, the received signal being generated by receiving thetransmitting signal transmitted from a transmitter, a demodulator that,in operation, generates a demodulated signal by demodulating the signal,which has been transmitted by modulating the N×Q/M constellation words;and a decoder that, in operation, decodes the demodulated signal inaccordance with the cyclic block permutation rule and the bitpermutation rule to generate data before coding according to thequasi-cyclic low-density parity check coding scheme.